1. Field of the Invention
This invention relates to seismic exploration and more particularly to a combination seismic cable for use in both marine and land exploration.
2. Discussion of the Prior Art
To fully understand the subsurface characteristics of the earth, seismic surveys must necessarily be conducted across many different environments. Many of the different environments require specific types of equipment to carry out the survey. In seismic exploration over the continental shelf, ships tow long liquid-filled plastic jackets containing hundreds of hydrophones. In bays, marshes, and along shorelines, small boats and buggies lay watertight, hardwired cables and hydrophones which are connected to a recording unit aboard a ship or marsh vehicle. Onshore seismic crews lay out complex arrays of detachable cables and geophones by truck and by foot.
Convention was that seismic cables designed for specific environments were not intermatable with cables designed for other environments. That is to say that a marine streamer could not be readily connected to a marsh cable and so on. Thus a marine seismic crew would survey as close to shore as possible at which point a bay crew would survey towards shore from where the ship could not. A separate seismic land crew would survey from the shoreline inland.
If a region including both land and marine environments needed to be surveyed simultaneously, two or more crews would have to work in concert. Often times, projects would run overtime because of the lack of synchronization between the crews. In some cases, seismic data would be duplicated by each crew.
A need exists for a seismic cable assembly that can be used both in shallow marine/marsh environments as well as on land. Traditional land cable systems have "takeouts" along the cable for detachably connecting other cables or geophones. Land cables are not suitable for use in water-covered environments because of leakage of water into the connectors. Traditional bay and marsh cable systems consist of a hydrophone and an integral impedance matching device such as a transformer encased in watertight housings hardwired to the cable. The labor involved in removing the hydrophones and re-wiring geophones in their place precludes the use of bay and marsh systems on land.
A conventional bay and marsh cable system provides a plurality of paralleling watertight connectors or "takeouts". The hydrophone and its integral impedance transformer previously mentioned are detachably connected to the cable at each takeout. For use on land, the hydrophone and transformer are disconnected from each takeout and one or more geophones are connected thereto.
In the conventional cable system the hydrophone or geophone must be physically removed from the cable to be rendered inactive. Attempts at deactivating a hydrophone by simply loosening the connector would result in water leakage into the connector.
It is an object of this invention to provide a seismic cable for use in marine/marsh and land seismic exploration.
It is another object of this invention to provide a seismic cable system where hydrophones and geophones may be rapidly connected to and disconnected from the cable.
It is yet another object of this invention to disconnect the hydrophones without physically removing them from the cable and connecting at least one geophone thereto.